If you've never flown your MAIII on anything larger than a D12-3, and you have access to a large enough field, you might want to give it a shot.
Estes E9 is a slow, majestic takeoff and longer burn --- very nice flight, but you want to have a long rod (around 6'), and no wind, because the rocket can weather cock into a breeze and head down range like a cruise missile. Some would say the motor is under-powered for that rocket, and if it's built heavy like mine, that's probably true, but under the right conditions, it's a nice flight.
Estes E12 has a stronger takeoff and straighter flight than the E9. Those two motors have almost the same impulse, but different thrust. So they go to almost exactly the same altitude, just at different speeds.
I've never had a Cato with an E9 or an E12, but I've seen a lot of them at club launches, and some people worry about it. An Aerotech single use E20 is a pretty awesome alternative. The MAIII really takes off with authority on that one, and it goes much higher that it does on the Estes motors.
If your field is small, stick with the D12, but if conditions allow it, you might want to try some of the other motors.